Changing engine oil is something all car owners deal with. But here's the dilemma—change it too early, and it feels like wasting money; change it too late, and the engine could suffer.

So, when's the best time to change the oil without wasting money or harming the car?

We need to consider a few key factors:

① How many miles we've driven since the last oil change

② How much time has passed since the last change

③ The driving environment, which can sometimes require special tools to determine the right time

How Many Miles Between Oil Changes?

Engine oils can be divided into three main types, each with a different mileage requirement.

1. Mineral Oil: Typically, it needs changing every 5,000 km. It's extracted from crude oil, has more impurities, and is cheaper. However, it oxidizes easily, making its lifespan shorter. It's also not ideal for cold climates due to its high freezing point.

2. Full Synthetic Oil: This oil is refined through complex chemical processes, making it high-quality and longer-lasting. It offers better fluidity, heat resistance, and oxidation stability than mineral oil. It usually lasts for 10,000 km before needing a change.

3. Semi-Synthetic Oil: This type is a blend of mineral and synthetic oils, usually in a 4:6 ratio. It offers performance close to full synthetic oil but costs a bit less. It typically needs to be changed every 7,500 km.

4. Long-Life Oil: While more common in foreign markets, it's not widely used in our country. The difference in fuel standards between our region and Western countries reduces its lifespan. Additionally, using long-life oil requires a long-life oil filter—if the filter gives out before the oil does, it can lead to issues.

How Long Before Oil Oxidizes?

After each service, mechanics usually write down the mileage and the next recommended service date, with "whichever comes first" as the rule. Why?

Even if the car doesn't run, oil can oxidize over time. For full synthetic oil, 12 months is usually the limit. After that, the oil loses its lubricating properties and may even accelerate engine wear, causing rust, overheating, and other problems.

For semi-synthetic and mineral oils, oxidation happens faster—usually within 6-9 months. If left unchanged beyond that, it can no longer protect the engine effectively.

How Can We Use Oil Test Paper?

Oil test paper is a simple tool that can help determine whether the oil needs changing.

Here's how to use it:

1. Remove the dipstick from the engine

2. Drip a few drops of oil onto the test paper

3. Leave it for 24 hours to let the oil fully spread

4. Observe the diffusion rings

If the edges of the rings are hard and dark, the oil has degraded and should be replaced. This simple test helps us judge the condition of the oil more accurately.

Which Oil Is Most Cost-Effective?

Knowing when to change oil is important, but choosing the right oil matters just as much. Full synthetic oil is top-quality but comes at a higher price and isn't necessary for all types of engines.

For small-displacement naturally aspirated engines, semi-synthetic oil is often sufficient. However, turbocharged engines perform best with full synthetic oil to meet their higher demands.

The best way to choose is to refer to the vehicle's manual. It provides recommendations for the correct oil type, helping us avoid unnecessary expenses. Remember, the most expensive oil isn't always the best—choosing the right one for our car's engine is what truly matters.

Bonus Tips for Oil Changes

We can adjust the oil change frequency depending on driving conditions. If we drive on smooth roads in dry weather, we can extend the change interval slightly. But in congested traffic or humid climates, it's best to shorten the interval.

Lykkers, have you been changing your engine oil at the right time? Keeping your car running smoothly is all about the little details!